There presently exists a significant need for a practical and economical means for treating both water and waste-water by means of filters. Typical prior art filtration generally involves vertical filtering through media such as sand and gravel. The grading and vertical distribution of said media varies according to the distribution of sizes such that when backwashed vertically the media expands upwardly but then settles back into place in a stratified or graded arrangement. This places the finest of the sand particles at the top of the filter column and the coarsest media at the bottom. Such a vertical filter column is easily plugged up because the fine sand in the topmost layers is the easiest layer to clog and is exposed to the heaviest burden of impurities. Plugging would be minimized if a course to fine grading could be used to permit removal of some of the larger suspended particles ahead of the fine sand layers. There is no way, given that specific gravities of the media layers are constant, for a backwash arrangement to deposit the coarser media on top of the finer media.
In addition, when backwash water does emerge from the surface of a sand bed into a larger void, there results a rapid deceleration of the effluent. This rapid deceleration can result in an immediate loss of sufficient velocity to deposit the heavier dirt particles with the result that these materials tend to accumulate on top of the filtering column such that plugging is enhanced and periodic maintenance is required.